The requirement of a high starting voltage is a well-known characteristic of discharge lamps. Some types of discharge lamps, such as high-intensity discharge (HID) lamps, require starting voltages on the order of several thousand volts.
The prior art teaches a number of ballasts and starting circuits for HID lamps. Many prior art ballasts have starting circuits that employ a pulse coil to generate a narrow high voltage pulse for igniting the lamp. Typically, the pulse coil is located in series with the lamp and must therefore be capable of handling the current that flows through the lamp after the lamp ignites. Because the lamp current is typically quite large (e.g., 700 milliamperes or more), the pulse coil must be wound with fairly large diameter wire in order to keep resistive power losses within a manageable limit and thereby preserve ballast efficiency. Consequently, the pulse coil may have considerable physical size and monetary cost.
"Pulse" type starting circuits typically require breakdown devices such as sidacs. Such devices add significant cost and/or complexity to the starting circuit, and may significantly detract from the overall reliability of the ballast. Moreover, "pulse" type starting circuits are usually ill-suited for use with remote installations in which the length of the wires between the lamp and ballast is more than a few feet. Due to the inherent capacitance of the wiring, the high frequency starting pulse may be significantly attenuated. Consequently, the lamp may not receive sufficient voltage to ignite.
What is needed therefore, is a ballast with a reliable, efficient, and cost-effective starting circuit that provides a high voltage for igniting discharge lamps, that does not require costly magnetics, switches, or breakdown devices, and that is well-suited for remote lamp applications. Such a ballast and starting circuit would represent a considerable advance over the prior art.